1. Field of the Invention
This invention relates to a solar-battery array comprising a plurality of solar batteries, and a photovoltaic power generation system having such a solar-battery array.
2. Related Background Art
In recent years, photovoltaic power generation systems have attracted notice as clean and new energy supply means. When they are used as power sources of outdoor signs or power sources of watches or clocks, in some cases a single solar cell (or a solar-cell module) and a secondary battery are combined to set up a photovoltaic power generation system. When, however, the photovoltaic power generation systems are employed in public institutional buildings, general houses, power plants and so forth, it is common to design a photovoltaic power generation system with an electric power of several kilowatts (kW) or more. On the other hand, the electric power per one solar cell or solar-cell module is usually several watts (W) to hundreds of W. Hence, in the photovoltaic power generation system for providing an electric power of several kW or more, it is common to use a solar-battery array consisting of a plurality of solar batteries.
Incidentally, those in which a plurality of solar batteries are connected in series are commonly called a solar-battery string and those in which a plurality of solar batteries or solar-battery strings are connected in parallel are often called solar-battery arrays in a narrow sense. In the present specification, when simply “solar-battery array” is termed, it is a concept which embraces the solar-battery string.
Also when simply “solar battery” is termed in the present specification, it is a concept which embraces both the solar cell and the solar-cell module. In the present specification, the “solar cell” is the smallest constituent unit of a device having the function of photoelectric conversion, and is meant to be such a unit that a photoelectric conversion device with a smaller electromotive force is substantially unable to be taken out without destroying the part pertaining to photoelectric conversion (usually, semiconductor layers) of the unit. Meanwhile, in the present specification, the term “solar-cell module” refers to a component in which a plurality of solar cells are electrically connected (e.g., connected in series or connected in parallel) into an integral body. To distinguish the “solar cell” from the “solar-cell module” is not essential in the most of the invention described in the present specification. Accordingly, the term “solar battery” is used as a concept which represents these collectively. As for the invention in which it has a meaning to distinguish them will be described later.
Now, in the large-power photovoltaic power generation system as stated above, there is risk of receiving an electric shock on touch with its electric circuit. In usual photovoltaic power generation systems, such an electric circuit is covered or the surroundings of power generation systems are forbidden to enter, to provide a countermeasure for the electric shock. However, if any covering material which covers the electric circuit is broken or when any execution or maintenance is performed, you may accidentally touch the electric circuit.
Meanwhile, as a method of lessening the effects on human bodies if you touch the electric circuit of a solar-cell array, a method is available in which e.g., a transformer (insulation transformer) is used to make perfect insulation between the whole electric circuits of the array and the ground (bring them into a state of floating) so that any loop of electric current may not be formed if you touch the electric circuit. Even in such a case, however, the effects on human bodies can not be controlled if you touch a different part of the electric circuit in the state a ground fault has unintentionally been formed at some part of the electric circuit.